Sobel Edge Detection 的shader实现

//-----------------------------------------------------------------------------


// Name: Sobel.fx


//


// Description:


//


//-----------------------------------------------------------------------------




//-----------------------------------------------------------------------------


// Effect File Variables


//-----------------------------------------------------------------------------




float4x4 worldViewProj : WorldViewProjection; // This matrix will be loaded by the application




texture testTexture; // This texture will be loaded by the application


const float Brightness = 1.0f;




sampler Sampler = sampler_state




...{


Texture = (testTexture);


MipFilter = LINEAR;


MinFilter = LINEAR;


MagFilter = LINEAR;


};




//-----------------------------------------------------------------------------


// Vertex Definitions


//-----------------------------------------------------------------------------




// Our sample application will send vertices


// down the pipeline laid-out like this...




struct VS_INPUT




...{


float3 position : POSITION;


float2 texture0 : TEXCOORD0;


};




// Once the vertex shader is finished, it will


// pass the vertices on to the pixel shader like this...




struct VS_OUTPUT




...{


float4 hposition : POSITION;


float2 texture0 : TEXCOORD0;


float4 color : COLOR0;


};




// And finally, the pixel shader will send a single


// color value to the frame buffer like this...




struct PS_OUTPUT




...{


float4 color : COLOR;


};




//-----------------------------------------------------------------------------


// Simple Vertex Shader


//-----------------------------------------------------------------------------




VS_OUTPUT myvs( VS_INPUT IN )




...{


VS_OUTPUT OUT;




OUT.hposition = mul( worldViewProj, float4(IN.position, 1) );




OUT.color = float4( 1.0, 1.0, 1.0, 1.0 ); // Pass white as a default color


//OUT.color = float4( 0.0, 1.0, 0.0, 1.0 ); // Pass green to test vertex shader




OUT.texture0 = IN.texture0;




return OUT;


}




//-----------------------------------------------------------------------------


// Simple Pixel Shader


//-----------------------------------------------------------------------------




PS_OUTPUT myps( VS_OUTPUT IN )




...{


PS_OUTPUT OUT;




// OUT.color = tex2D( Sampler, IN.texture0 ) * IN.color;




// If you uncomment the next line, the color passed to us by our


// vertex shader and the selected texture sampler will be ignored


// completely and all output to the frame buffer will be blue regardless.




//OUT.color = float4( 0.0, 0.0, 1.0, 1.0);






const int NUM = 9;


const float threshold = 0.09;


const float texW = 140.f;


const float texH = 140.f;




//round texels




const float2 c[NUM] =...{


float2( -1/texW,1/texH),


float2( 0.00, 1/texH),


float2( 1/texW, 1/texH),


float2( -1/texW,0.00),


float2( 0.00, 0.00),


float2( 1/texW, 1/texH ),


float2(-1/texW, -1/texH),


float2( 0.00 , -1/texH),


float2( 1/texW, -1/texH),


};




float3 col[NUM];


int i;




//it stores the samples of texture to col array.






for (i=0; i < NUM; i++) ...{


col[i] = tex2D(Sampler, IN.texture0 + c[i]);


}




//now we start to compute the luminance with dot product and store them in lum array.


//lum = 0.30r + 0.59g + 0.11b;


float3 rgb2lum = float3( 0.30, 0.59, 0.11);




float lum[NUM];




for (i = 0; i < NUM; i++) ...{


lum[i] = dot(col[i].xyz, rgb2lum);




}




//Sobel filter computes new value at the central position by sum the weighted neighbors.




float x = lum[2]+ lum[8]+2*lum[5]-lum[0]-2*lum[3]-lum[6];


float y = lum[6]+2*lum[7]+ lum[8]-lum[0]-2*lum[1]-lum[2];




//show the points which values are over the threshold and hide others. Final result is the


//product of col[5] and edge detector value. Brightness adjusts the brightness of the image.




float edge =(x*x + y*y < threshold)? 1.0:0.0;




//final output




OUT.color.xyz = Brightness * col[5].xyz * edge;


OUT.color.w = 1.0;




return OUT;


}




//-----------------------------------------------------------------------------


// Simple Effect (1 technique with 1 pass)


//-----------------------------------------------------------------------------




technique Technique0




...{


pass Pass0




...{


Lighting = FALSE;




Sampler[0] = (Sampler); // Needed by pixel shader




VertexShader = compile vs_2_0 myvs();


PixelShader = compile ps_2_0 myps();


}


}





效果图：





参考文档：

http://homepages.inf.ed.ac.uk/rbf/HIPR2/sobel.htm

http://www.pages.drexel.edu/~weg22/edge.html

http://www.neatware.com/lbstudio/web/hlsl.html